Method and device for purifying untreated water

ABSTRACT

The invention relates to the purification of untreated water which is polluted with dissolved organic carbon compounds which can be biologically or adsorptively removed in a three-step process, whereby the upstream purification step is predominantly biological, i.e. operates as a biofilter ( 1 ), and both subsequent purification steps are predominantly adsorptive in nature, i.e. operate as adsorbers ( 2, 3 ). The biofilter ( 1 ) is purified by backwashing, whereby the backwashing periods occur according to the TOC determined between the biofilter ( 1 ) and the upstream adsorber ( 2 ) and/or running time and/or pressure loss. The upstream adsorber ( 2 ) is also cleaned by backwashing and is subsequently shifted into a downstream position alternating with the other adsorber ( 3 ). The method is suitable for obtaining TOC concentrations in treated water of less than 500 ppb.

[0001] The invention relates to a method as well as an apparatus for thepurification of untreated water that is polluted with substances,especially dissolved organic carbon compounds, that can be biologicallyand adsorptively removed, especially for the preliminary purification ofchlorine-free drinking water as a preliminary step for the production ofhigh-purity water from which minerals and salts have been completelyremoved.

[0002] It is an object of the invention to enable a particularlyeffective and hence particularly economical purification of theuntreated water.

[0003] To accomplish this, the invention proposes,

[0004] that the purification is carried out in three stages,

[0005] that the upstream purification stage is operated predominantlybiologically as a biofilter, and the subsequent purification stages areoperated predominantly adsorptively as adsorbers,

[0006] that the biofilter is cleaned by backwashing, whereby thebackwash periods are initiated as a function of the TOC determinedbetween the biofilter and the upstream adsorber and/or as a function ofthe running time and/or as a function of the pressure loss over thebiofilter, and

[0007] that the upstream adsorber is cleaned by backwashing and is thenshifted to the downstream position by alternating it with the otheradsorber.

[0008] Biofilters for the purification of untreated water, for examplefor the production of drinking water, are known. It is also known to useadsorbers for the water purification. In both cases one operates withactivated carbon, as is also preferably the case with the presentinvention. The effectiveness of the known methods is, however, limited.In addition, the activated carbon must frequently be exchanged,resulting in a considerable cost burden. Also known is the use ofmicrofilters, whereby these filters allow a very high degree ofeffectiveness to be achieved. They are even suitable for producing ultrapure water, as is required for the manufacture of chips. However, thecosts for carrying out a microfiltration are extremely high.

[0009] The inventively proposed 3-stage method is in a position toachieve a high degree of effectiveness at a relatively low cost. Themethod serves primarily as a preliminary stage for the production ofhigh-purity water for industrial use. Involved is a closed process withwhich only easily usable residues result. The method is suitable forachieving TOC concentrations in processed water of <500 ppb.

[0010] The untreated water is conditioned in such a way that in thebiofilter a high biological activity is achieved that is enhanced by anextensively constant hydraulic charge. The biofilter is monitored bydetermining the TOC (TOC stands for Total Organic Carbon) in thefiltrate. As soon as the TOC has risen to a prescribed value, abackwashing of the biofilter is effected. A break-through of TOC to theupstream adsorber can thus be effectively prevented. There is also noblockage of the biofilter. The backwashing reduces the solidcontent/biomass to the respective minimum quantities that are requiredfor the reliable functioning of the biofilter. The activated carbon ofthe biofilter does not need to be exchanged. In addition, oralternatively to the TOC monitoring, the backwashing of the biofiltercan also be initiated as a function of the running time (determined bythe throughput) or as a function of the pressure loss over thebiofilter.

[0011] The subsequent, upstream adsorber is also backwashed, and isthereby protected against premature depletion. It serves to receive andto adsorb the slippage of TOC and impurities that occurs in thebiofilter. The upstream adsorber has only a very slight biologicalfunction. Its effectiveness is predominantly an adsorption function toreduce the adsorptively removable TOC. As a consequence of thebackwashing, the activated carbon is kept in a mechanically clean stateand remains effective for a long period of time, so that an exchange isrequired only at very great time intervals. This contributesconsiderably to the economy of the inventive method.

[0012] The downstream adsorber enables not only an optimization of thepurification process, but rather also permits a nearly constant andcontinuous maintenance of a very high effectiveness. In particular, ifthe upstream adsorber is cleaned, the downstream adsorber takes over itsfunction. It thus becomes the upstream adsorber, where upon the freshlycleaned adsorber assumes the downstream position, and now in turnoptimizes the purification process. The shift or alternation enables ahigh and constant adsorption efficiency and the utilization of the fulladsorption capacity of both of the adsorbers.

[0013] A preferred application of the invention is the pre-purificationduring the production of high-purity water from which salts and mineralsare completely removed, as it is used, for example, as process water inindustrial processing engineering and the chemical industry, or also asfeed water for boiler plants. Following the purification is a salt ormineral removal stage that operates as reverse osmosis or ion exchange.

[0014] An important recognition that lies at the basis of the inventionis that after the removal of chlorine, the growth of micro organismsincreases suddenly due to the increased substrate content. Without theeffective reduction of substrate concentration made possible by theinvention, there would thus result an impermissible contamination of thedownstream unit for removing salt and minerals due to germination andbiofouling. In the biofilter, the substrate concentrations aremineralized and are converted into the biomass or into other substances.These and non-assimilated substances (TOC slippage) are adsorbed in thesubsequent adsorbers.

[0015] By means of suitable conditioning measures, primarily byregulating the temperature and the oxygen content, a high biologicalactivity is maintained in the biofilter. With a relatively long contacttime, there results a reduction of the predominantly biologicallyremovable TOC. The subsequent adsorbers reduce the adsorptivelyremovable TOC.

[0016] The biofilter can be built up during the operation. Moreadvantageous is to use an already seeded filter.

[0017] As a further development of the invention, it is proposed thatthe backwashing of the biofilter be synchronized with the backwashing ofthe upstream adsorber. During the backwashing of the biofilter, theupstream adsorber should be ready for use, so that in cooperation withthe downstream adsorber it can briefly help assume the function of thebiofilter. The time control is in this connection preferably such thatthe shifting of position of the two adsorbers has taken place shortlybefore the backwashing of the biofilter is carried out.

[0018] It can furthermore be advantageous to initiate the backwashperiods of the upstream adsorber as a function of the TOC that isdetermined between this adsorber and the downstream adsorber. Thebackwash periods of the upstream adsorber, and possibly synchronouslytherewith the backwash periods of the biofilter, can thus also beinitiated as a function of the loading of the upstream adsorber. Thisprevents an overloading of the downstream adsorber.

[0019] The reliability of the purification process can additionally beincreased by additionally or alternatively initiating the backwashingperiods as a function of the pressure loss determined over the upstreamadsorber.

[0020] Each of the backwashing periods preferably includes a lowering ofthe water level in the biofilter or in the upstream adsorber, and then abackwashing with air and/or with water. After the lowering of the waterlevel, it is particularly advantageous to first loosen the activatedcarbon with air, so that a subsequent backwashing with water results ina particularly high degree of effectiveness. This is of particularsignificance with regard to the time required for the backwashing.Finally, during the backwashing the three-stage purification process isreduced to a two-stage process.

[0021] Pursuant to a significant further development of the invention,it is proposed that during times that are free of a removal of water,the biofilter be separated from the upstream adsorber, and the twoadsorbers be switched off.

[0022] Frequently, for example on weekends and holidays, there is noneed to make purified or pre-purified water available. In thisconnection, the unit cannot be switched off, since otherwise thebiofilter would be adversely affected. However, if during the times thatare free of water removal one would charge the adsorbers with thefiltrate of the biofilter, the inherently produced purified orpre-purified water would have to be discarded. After switching off theadsorbers, it is merely necessary to re-circulate the filtrate of thebiofilter. It is of particular significance that during the times thatare free of water removal the adsorbers in no way be charged by thefiltrate of the biofilter. This increases the time spans between thebackwash periods of the upstream adsorber, and extends the service lifeof the activated carbon filling of the two adsorbers.

[0023] During the times that are free of the removal of water, thebiofilter, which is separated from the upstream adsorber, is preferablyoperated with a reduced throughput, since this is sufficient formaintaining the biological activities.

[0024] Thus, the invention makes it possible to avoid the TOC slippagethrough the entire unit. The danger of a bacterial contamination ofdownstream components of the unit is greatly reduced. The same appliesfor the blockage of functional groups of the ion exchange resin of theunit for the complete removal of salt and minerals. The operating costsare reduced, and only easily usable residues are produced.

[0025] The invention furthermore provides an apparatus for carrying outthe previously described method, namely for the purification ofuntreated water that is polluted with substances, especially dissolvedorganic carbon compounds, that can be biologically and adsorptivelyremoved, especially for the preliminary purification of drinking waterfrom which chlorine has been removed as a preliminary step for theproduction of high-purity water from which minerals and salts have beencompletely removed, whereby this apparatus has the following features:

[0026] a feed line for untreated water,

[0027] a drain line for purified water,

[0028] a biofilter, the inlet of which is connected to the feed line foruntreated water,

[0029] a first and a second adsorber, the inlets of which areconnectable to the feed line for untreated water and to the outlet ofthe biofilter, and the outlets of which are connectable to the drainline for purified water, whereby furthermore the outlet of the firstadsorber is connectable to the inlet of the second adsorber and theoutlet of the second adsorber is connectable to the inlet of the firstadsorber

[0030] a feed line as well as a drain line for backwash water and/or afeed line for backwash air, whereby the lines are connectable to thebiofilter as well as to each of the two adsorbers, and

[0031] a control device for the operation of the valves that areassociated with the biofilter and each of the two adsorbers, whereby thecontrol device is connected with a TOC measurement location on theoutlet of the biofilter and/or with a throughput measurement deviceand/or with a differential pressure measurement device for thebiofilter.

[0032] Further preferred features are provided in the dependent claims.

[0033] The invention will be explained in greater detail subsequentlywith the aid of a preferred embodiment in conjunction with theaccompanying drawing. The drawing shows in:

[0034]FIG. 1 a control diagram of an apparatus for the purification ofuntreated water.

[0035] Pursuant to FIG. 1, a biofilter 1 is provided which is followedin series by two adsorbers, namely a first adsorber 2 and a secondadsorber 3. The inlet of the biofilter 1 is connected to a feed line 4for untreated water, whereby it is advantageous to introduce oxygen intothe inlet in a controlled manner in order to avoid an under supply ofoxygen to the micro organisms. Furthermore, the outlet of the secondadsorber 3 is connected to a drain line 5 for purified water. Thetemperature of the feed of the biofilter is preferably monitored andregulated.

[0036] The diagram of FIG. 1 shows in heavy, solid lines one of thepaths that the water can take from the feed line 4 for untreated waterthrough the biofilter 1 and the two adsorbers 2 and 3 to the drain line5 for purified water. In accordance therewith, the adsorber 2 operatesas an upstream adsorber. It adsorbs a significant portion of the TOCthat overflows out of the biofilter 1. Its biological activity isslight. Emphasized is its adsorption capacity.

[0037] The downstream adsorber 3 optimizes the purification process and,after appropriate shifting, takes over the function of the upstreamadsorber, while the first adsorber is backwashed and is then shifted tothe downstream position.

[0038] Provided at the outlet of the biofilter 1 is a TOC measurementlocation 6. It is in communication with a non-illustrated control devicethat operates the plurality of valves that are associated with the unit.As soon as the TOC measurement location 6 indicates a preselected value,the biofilter 1 is shifted to backwash.

[0039] The backwash system includes a feed line 7 and a drain line 8 forbackwash water, as well as a feed line 9 for backwash air.

[0040] The backwashing of the biofilter 1 is initiated by closing itsinlet and its outlet. A line section 20 serves as a bypass and connectsthe inlet of the first adsorber 2 with the feed line 4 for untreatedwater. The water level in the biofilter 1 is then lowered, and inparticular via a line section 11 that connects its outlet with the drainline 8 for backwash water. There is then effected a loosening of theactivated carbon in the biofilter 1. For this purpose, the latter isconnected via a line section 12 to the feed line 9 for backwashed air.Venting can be effected into the drain line 8 for backwash water. As thelast step, the biofilter 1 is connected via a line section 13 to thefeed line 7 for backwash water. As soon as the cleaning process isterminated, the original operation is again undertaken.

[0041] As an additional safety measure, the biofilter 1 is provided witha differential pressure measurement device 14 that is connected to thecontrol device and ensures that the backwashing of the biofilter 1 isstarted even if the pressure drop over the biofilter exceeds aprescribed maximum value.

[0042] The backwashing of the two adsorbers 2 and 3 is carried out in acorresponding manner. The components required to accomplish this thatcoincide with those of the biofilter 1 have reference numerals in thehundreds for the adsorber 2 and in the two hundreds for the adsorber 3.

[0043] The backwashing of the upstream adsorber, which according to thecontrol diagram illustrated in heavy, solid lines in FIG. 1 is the firstadsorber 2, can be effected synchronously with the backwashing of thebiofilter 1, although under the condition that the latter is inoperation. As a first step, the inlet of the adsorber 2 is closed,whereby at the same time the inlet of the adsorber 3 is connected to theoutlet of the biofilter 1, and in particular via a line section 15.

[0044] The adsorber 3 now takes over the entire adsorption capacity.After its outlet is closed, the adsorber 2 is backwashed in the same wayas was described in conjunction with the biofilter 1.

[0045] After conclusion of the backwashing of the adsorber 2, it isconnected downstream of the adsorber 3. The latter thus obtains itsupstream position, while the adsorber 2 assumes the downstream position.For this purpose, the connection between the outlet of the adsorber 3and the drain line 5 for purified water is interrupted. Instead, theoutlet of the adsorber 3 is connected to the inlet of the adsorber 2,and in particular via a line section 16. The now again opened outlet ofthe adsorber 2 is connected via a line section 17 with the drain line 5for purified water. At the appropriate time, the now upstream adsorber 3is backwashed in the same manner as was described in connection with thebiofilter 1.

[0046] On days that are free of the withdrawal of water (e.g. weekendsand holidays) no purified water is needed. One separates the outlet fromthe biofilter 1 from the drain line 5 for purified water, and connectsit to a removal line 18. At the same time, the throughput of thebiofilter 1 is reduced, preferably to approximately one third of thenormal operating throughput.

[0047] For the emergency situation where both of the adsorbers 2 and 3are disrupted, a bypass line 20 is provided that connects the outlet ofthe biofilter 1 directly to the drain line 5 for purified water.

[0048] The method of the invention is preferably operated with aconstant throughput capacity. This leads to optimal contact times and toa defined mass transfer. It was discovered that a reduction of the TOCvalue to approximately 500 ppb could be achieved. This is an averagevalue that is subjected to only slight fluctuations. The invention thusenables very long service lives in combination with a very high TOCreduction.

[0049] Various modification possibilities are within the scope of theinvention. For example, the separate removal line 18 for the biofilter 1can be eliminated if a possibility is provided for connecting the outletof the biofilter 1 to the drain line 8 for backwash water. Furthermore,one can dispense with the use of backwash air if no loosening of theactivated carbon is desired. Alternatively, the possibility exists forcarrying out the backwashing with only air,. The synchronization of theupstream adsorber with the backwashing of the biofilter can be a fixedcoupling determined by a time interval. It is then possible to dispensewith the TOC measurement locations 106 and 206 as well as with thepressure differential devices 114 and 214. The operation is moreflexible if merely the sequence of the backwashing processes ismaintained. The exchange of the activated carbon of the two adsorberscan be integrated into the backwash cycles. It is not necessary toexchange the activated carbon of the biofilter.

[0050] As a modification of the described unit, it is possible to carryout the backwashing of the biofilter and/or of the upstream adsorberonly as a function of the running time or only as a function of thebuild up of the respective pressure drop. However, the TOC measurementhas proven to be a very reliable control. The mechanical cleaning of theadsorbers is, as mentioned, preferably carried out first with air andsubsequently with water. A purely air or water backwashing is, as alsoalready mentioned, likewise possible.

1. Method for the purification of untreated water that is polluted withsubstances, especially dissolved organic carbon compounds, that can bebiologically and adsorptively removed, especially for the preliminarypurification of chlorine-free drinking water as a preliminary step forthe production of high-purity water from which minerals and salts havebeen completely removed, whereby the purification is carried out inthree stages, the upstream purification stage is operated predominantlybiologically as a biofilter, and the subsequent purification stages areoperated predominantly adsorptively as adsorbers, the biofilter iscleaned by backwashing, whereby the backwash periods are initiated as afunction of the TOC determined between the biofilter and the upstreamadsorber and/or as a function of the running time and/or as a functionof the pressure loss over the biofilter, and the upstream adsorber iscleaned by backwashing and is then shifted to the downstream position byalternating it with the other adsorber.
 2. Method according to claim 1,characterized in that the backwashing of the biofilter is synchronizedwith the backwashing of the upstream adsorber.
 3. Method according toclaim 1 or 2, characterized in that the backwash periods of the upstreamadsorber are initiated as a function of the TOC determined between thisadsorber and the downstream adsorber.
 4. Method according to claim 3,characterized in that the initiation of the backwash periods isadditionally or alternatively effected as a function of the pressureloss determined over the upstream adsorber.
 5. Method according to oneof the claims 1-4, characterized in that each backwash period includes alowering of the water level in the biofilter or in the upstreamadsorber, and then a backwashing with air and/or with water.
 6. Methodaccording to one of the claims 1-5, characterized in that during timesthat are free of the removal of water, the biofilter is separated fromthe upstream adsorber and the two adsorbers are shut off.
 7. Methodaccording to claim 6, characterized in that the biofilter that isseparated from the upstream adsorber is operated at a reducedthroughput.
 8. Apparatus for carrying out the method of one of theclaims 1 to 7, namely for the purification of untreated water that ispolluted with substances, especially dissolved organic carbon compounds,that can be biologically and adsorptively removed, especially for thepreliminary purification of chlorine-free drinking water as apreliminary stage for the production of high-purity water from whichsalts and minerals have been completely removed, whereby the apparatushas the following features: a feed line (4) for untreated water, a drainline (5) for purified water, a biofilter (1), the inlet of which isconnected to the feed line (4) for untreated water, a first and a secondadsorber (2,3), the inlets of which are connectable to the feed line (4)for untreated water and to the outlet of the biofilter (1), and theoutlets of which are connectable to the drain line (5) for purifiedwater, whereby furthermore the outlet of the first adsorber (2) isconnectable to the inlet of the second adsorber (3) and the outlet ofthe second adsorber (3) is connectable to the inlet of the firstadsorber (2), a feed line as well as a drain line (7,8) for backwashwater and/or a feed line (9) for backwash air, whereby the lines (7-9)are connectable to the biofilter (1) as well as to each of the twoadsorbers (2,3), and a control device for the operation of the valvesthat are associated with the biofilter (1) and each of the two adsorbers(2,3) whereby the control device is connected to a TOC measurementlocation (6) at the outlet of the biofilter (1) and/or to a throughputmeasurement device and/or to a differential pressure measurement device(14) for the biofilter (1).
 9. Apparatus according to claim 8,characterized in that a TOC measurement location (106,206) that isconnected with the control device is provided at the outlet of each ofthe two adsorbers (2,3).
 10. Apparatus according to claim 8 or 9,characterized in that each of the two adsorbers (2,3) is provided with adifferential pressure measurement device (114,214) that is connected tothe control device.
 11. Apparatus according to one of the claims 8 to10, characterized in that the outlet of the biofilter (1) is connectableto a removal line (18).
 12. Apparatus according to one of the claims 8to 11, characterized by a re-circulation line (19) that is connected tothe drain line (5) for purified water and that is connectable to theinlet of each of the two adsorbers (2,3).